1. Field of the Invention
The present invention relates to sound transmission barriers and sound adsorption media systems that are especially useful in motor vehicles and boats.
2. Description of the Prior Art
The standard sound transmission barrier system used in motor vehicles and boats relies on a multi-layered structure that has either one or two intermediate layers of an impermeable (i.e., to air) material with a high mass per unit area. When two intermediate layers are used, the intermediate layers are in direct contact with each other in the final barrier system. The intermediate layer(s) is(are) sandwiched between a relatively soft lower layer and an upper layer that is exposed to the environment.
Traditionally, the lower layer contacts the inner surface of the structural skin of the motor vehicle or boat (e.g., the sheet metal of an automobile or the wood, metal or fiberglass hull of a boat). The lower layer is usually formed from an inexpensive fibrous material, such as "shoddy" (a layered material composed primarily of textile scraps and manufactured by a number of companies, including Jamesville Products Company and Chris Craft Company).
Usually the intermediate layers are formed from a thermoformable material. "Massback" has been widely used in the automobile industry for this purpose. A relatively dense material, normally impermeable to air and thermoformable, massback can be formed from virtually any plastic or rubber material which contains a high-mass filler material. The preferred composition of massback includes EVA (ethylene-vinylacetate copolymer), polyethylene, PVC (polyvinylchloride) or tar as the base thermoplastic material, and a high-mass filler material, such as calcium carbonate or barium sulfate, added to increase the mass.
The upper layer of the traditional sound transmission barrier is either carpet or some other surface material that may be exposed to the environment (e.g., vinyl or a plastic material). When the lower, intermediate and upper layers are arranged in the manner indicated above, they provide a sound transmission barrier which reduces the amount of outside noise that would otherwise reach the cabin interior of the motor vehicle or boat.
Although the prior art sound transmission barrier systems are effective in reducing the amount of outside noise that reaches the interior of the motor vehicle or boat, there has been a long-felt need to reduce the overall weight of the systems without decreasing the effectiveness of the systems as sound transmission barriers and/or sound absorption media. This need has been satisfied by the sound transmission barrier and sound absorption media systems of the present invention.